Michael Phelps Faces His Toughest Challenger Yet - Age

Michael Phelps is participating in his fifth Summer Olympics, a U.S. record among male swimmers. He's already won 23 medals, including a record-setting 19 golds - including a gold with the 4x100-meter freestyle relay team Sunday night - and could add three more in Rio when he competes in the 100-meter butterfly, the 200-meter butterfly and the 200-meter individual medley.

And winning an individual Olympic medal in a swimming event at the age of 31 might be even more impressive than racking up that record-setting medal count.

Phelps turned 31 in June, which makes him super old in terms of competitive swimming. Over the past 10 Summer Games, the oldest athlete to swim in the finals for the same events in which Phelps is scheduled to compete has been 29 years old, with the average age just under 22 years old. And, not surprisingly, times get slower as an athlete ages.

However, Phelps is no ordinary athlete. His best time of 50.6 seconds in the 100-meter butterfly from the 2008 Summer Games in Beijing as a 23-year-old is only four-tenths of a second better than his best time at the 2016 U.S. trials as a 31-year old (51 seconds). Dating back to 1976, the best time by any Olympic swimmer in the 100-meter butterfly over the age of 30 was Adam Pine in 2008 (52.1 seconds at 32 years old), 1.4 seconds faster than the average speed for that age group. In fact, Phelps's U.S. trials time is 2.8 seconds faster than the average time for Olympian swimmers in the 24-to-28 year-old age bracket.

His biggest competition in the 100- and 200-meter butterfly events is expected to come from South Africa's Chad Le Clos and Hungary's Laszlo Cseh Jr.

Le Clos, who turned 24 years old in April, tied for silver in 2012 in this event, losing to Phelps by 0.13 seconds. Le Clos clocked a time of 51.82 at the 2016 South African nationals, but his best time in this event since the Summer Games in London is 50.56 seconds in 2015.

Cseh doesn't have the same renown as Phelps, but he is nearly as impressive - particularly given what he's done in the latter stages of his career. A medalist at every Olympics since he first represented Hungary at the 2004 Olympic Games in Athens, Cseh turned 30 in December and set a meet record for the fastest 100-meter butterfly time at the European championships (50.86). To have one swimmer in his 30s contend for a medal is unheard of. The fact that two could be on the podium illustrates that this could be one of the rarest events in Olympic history.

According to Lauren Neidigh of swimswam.com, Phelps and Le Clos, a swimmer seven years his junior, are projected to post the two best times of the event at 50.3 and 50.4 seconds, respectively. Cseh is expected to battle for bronze with a predicted time of 50.7 seconds.